查询以使用外键获取行值（first_name 和 last_name）

Question

New to SQL and MySQL.

In the below table, I've a table of employees where emp_id is employee's ID & super_id is supervisor's employee ID. Here super_id is assigned as foreign key of employee table itself.

Now I need to fetch a table with three columns: first_name (supervisor), last_name (supervisor) and Count of employees who are supervised by this employee.

For Example:

David     Wallace   3
Michael   Scott     3
Josh      Porter    2

Thanks in advance

Answer 1

This is a self-join:

select tsuper.first_name, tsuper.last_name, count(*)
from t join
     t tsuper
     on t.super_id = tsuper.emp_id
group by tsuper.first_name, tsuper.last_name;